I really like science fiction and fantasy films. Almost every film I watch is either that or action. However, I've noticed there are a lot of films in this genre that have practically no substance and that is a personal pet peeve of mine. I prefer movies that have an actual story line rather than just looking for excuses to have action scenes.
For sure I had to pick the sci-fi/fantasy followed closely by action/adventure. Most of the movies I really like the most have both of those elements in them. In my opinion Star Wars is hands down the best!
It's difficult to just choose one because it all depends on what kind of mood I'm in and whom I'm with when watching. If I'm with friends I tend to go comedy. If I'm alone I usually pick a drama and if I'm with someone special then a thriller. Probably doesn't make sense I know but its better to mix and match don't you think?
I tend to prefer science fiction or fantasy. I love movies with action in them, I have to agree with Joshua though as I like a story line and not just the action. Some of my favorite movies are: Lord of the rings, Harry Potter, etc.
I'm flexible, I can appreciate most things but I am partial to a good romantic comedy or well thought out drama. Thrillers are good too once they are not generic with expected endings.